In conditional access structures such as parking structures and the like, industrial gates are used to control the entrance and exit of vehicles. These industrial gates typically include a movable gate arm, pivotally attached at one of its ends to a gate support. The gate arm may be designed to prevent the unauthorized entrance or exit of a vehicle through a defined pathway of the structure. Upon the occurrence of an event, such as by payment of an access fee or by authorization of the vehicle by security personnel, the gate arm rotates out of the pathway to permit passage of the vehicle. The security gate itself sometimes includes one or more co-acting pieces, and is typically fabricated of wood, metal or other appropriate material. The length and therefore the weight of the gate arm vary depending on the dimension of the pathway in which the security gate is placed.
Industrial-type security gates are sometimes automated through the use of sensing apparatus for detecting approaching and departing traffic. The sensing apparatus usually includes inductive vehicle sensor loops embedded in the roadway at a spaced location relative to the security gate. Thus, when a vehicle approaches the security gate, the signal generated by the vehicle sensor may cause the gate to be automatically operated based on the sensing of a vehicle in the defined area. Alternatively, vehicle sensors are sometimes used in conjunction with a vending mechanism that is adapted to require the tender of a magnetic card, ticket, cash amount or the like. In many of these arrangements, the gate is operable to permit passage of the vehicle upon a sequential sensing of the vehicle and an authorization such as through payment or through a card reader.
U.S. Pat. No. 3,975,861 to Baump et al., entitled “Automated Parking Gate and Controls” discloses a security gate of the general type discussed above. The disclosed security gate includes a movable, elongate blocking arm that is lifted or lowered to permit vehicle entrance to and exit from a parking structure. To operate the security gate, a reversing alternating current (AC) electric drive motor is actuated upon the receipt of control signals from rather rudimentary logic circuitry. In particular, the logic circuitry provides signals to reverse or cease operation of the motor upon a sensing of certain conditions, such as when the gate strikes an object. This arrangement prevents unintended closure on vehicles or pedestrians entering the structure.
Security gates known in the art to this point, such as the gate disclosed by Baump et al., suffer from various drawbacks. For example, presently known security gates typically employ AC induction motors that supply torque to a gate arm moving mechanism to lift and lower the security gate arm. The induction motor size, voltage rating and operating frequency, as well as the gear reduction ratio of the motor output, are chosen as a function of the size and weight of the security gate arm. Since different geographical regions supply AC power at different voltages and at different frequencies, the same AC induction motor cannot be universally used for a security gate intended to be installed at different locations. For example, the typical AC power supply in the United States provides 120 or 240 volts at 60 cycles per second. In Europe, the typical AC power supply is 240 volts at 50 cycles per second. To summarize, the selection and design of components such as the AC induction motor and reduction or drive gear mechanisms must now be customized for each security gate installation based on such factors as the intended geographical location of installation, the dimension of the gate arm, and the weight of the gate arm.
To avoid injury to humans or damage to other objects, most security gate installations include a number of sensors. For example, a contact or proximity sensor is usually placed on the gate arm leading edge to detect whether the gate contacts or is in close proximity with a vehicle or other object. When the sensor detects such an obstruction, a signal is generated to direct the gate arm to be stopped or to reverse movement. Alternatively, or in addition to contact sensor arrangements, presently known gates sometimes use a current sensor for this purpose. The current sensor detects relative changes in motor current such as would be the case when the gate strikes an object as it is lowered. These sensors, however, add complexity to the design of the security gate. Additionally, they provide additional possible failures in the operation of the security gate.
Many security gates also include a mechanism to prevent the gate arm from being lifted either by accident or without authorization. In some security gates, internal motor rotor friction, as applied through a gearbox reducer, prevents the gate arm from being unintentionally or improperly lifted. At the same time, however, the security gate must be designed such that vehicles can still enter and exit the structure when power to the security gate is lost. To this end, security gates sometimes include a mechanism for automatically raising the gate arm in the event of a power loss.